Middle-low-temperature oxidation and adsorption of arsenic from flue gas by Fe–Ce-based composite catalyst

Fe-Ce-based composite catalysts were prepared and used for As2O3 catalytic oxidation and adsorption. They were characterized by XRD, BET, H2-TPR, Raman, SEM and XPS. The results suggests Fe, La and Zr can be partially doped into CeO2 lattice to form solid solutions. Compared with pure Fe2O3, the composite catalysts have stronger low-temperature reducibility, especially La3+ doping is beneficial to the formation of more low-temperature active sites. Raman and XPS measurements disclose the presence of oxygen vacancy and surface adsorbed oxygen in composite catalysts and these are more prominent in FeCeLaO. Ce3+ ratio increases to 18.30% after reaction, which confirms part of Ce4+ can participate in As2O3 oxidation and be reduced to Ce3+. The oxidation and adsorption capacity for As2O3 were investigated at different temperatures and O2 concentrations. The results show FeCeLaO exhibits excellent activity at middle-low-temperatures of 200-400 °C, the oxidation efficiency of As2O3 can reach 100%, the total adsorbed arsenic at 400 °C reaches 583.7 μg/g, which is 1.8 times of pure Fe2O3 at 600 °C. As2O3 oxidation mechanism over FeCeLaO with/without O2 was proposed through the Mars-Maessen theory with the aid of surface-active oxygen. The abundant oxygen vacancy defects and active chemisorbed oxygen play important roles and guarantee an efficient As2O3 oxidation, which is also the essential reason why the composite catalysts can effectively oxidize and adsorb As2O3 at middle-low-temperature of 200-400 °C, while pure Fe2O3 can only be at high temperature of 600-700 °C.